KVM: arm64: Add ARM64_KVM_PROTECTED_MODE CPU capability

Expose the boolean value whether the system is running with KVM in
protected mode (nVHE + kernel param). CPU capability was selected over
a global variable to allow use in alternatives.
Signed-off-by: David Brazdil <dbrazdil@google.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20201202184122.26046-3-dbrazdil@google.com

arch/arm64/include/asm/cpucaps.h

@@ -65,7 +65,8 @@
 #define ARM64_MTE				57
 #define ARM64_WORKAROUND_1508412		58
 #define ARM64_HAS_LDAPR				59
+#define ARM64_KVM_PROTECTED_MODE		60
 
-#define ARM64_NCAPS				60
+#define ARM64_NCAPS				61
 
 #endif /* __ASM_CPUCAPS_H */

arch/arm64/include/asm/kvm_host.h

@@ -58,6 +58,7 @@ enum kvm_mode {
 	KVM_MODE_DEFAULT,
 	KVM_MODE_PROTECTED,
 };
+enum kvm_mode kvm_get_mode(void);
 
 DECLARE_STATIC_KEY_FALSE(userspace_irqchip_in_use);
 

arch/arm64/include/asm/virt.h

@@ -97,6 +97,14 @@ static __always_inline bool has_vhe(void)
 		return cpus_have_final_cap(ARM64_HAS_VIRT_HOST_EXTN);
 }
 
+static __always_inline bool is_protected_kvm_enabled(void)
+{
+	if (is_vhe_hyp_code())
+		return false;
+	else
+		return cpus_have_final_cap(ARM64_KVM_PROTECTED_MODE);
+}
+
 #endif /* __ASSEMBLY__ */
 
 #endif /* ! __ASM__VIRT_H */

arch/arm64/kernel/cpufeature.c

@@ -74,6 +74,7 @@
 #include <asm/cpufeature.h>
 #include <asm/cpu_ops.h>
 #include <asm/fpsimd.h>
+#include <asm/kvm_host.h>
 #include <asm/mmu_context.h>
 #include <asm/mte.h>
 #include <asm/processor.h>
@@ -1703,6 +1704,21 @@ static void cpu_enable_mte(struct arm64_cpu_capabilities const *cap)
 }
 #endif /* CONFIG_ARM64_MTE */
 
+#ifdef CONFIG_KVM
+static bool is_kvm_protected_mode(const struct arm64_cpu_capabilities *entry, int __unused)
+{
+	if (kvm_get_mode() != KVM_MODE_PROTECTED)
+		return false;
+
+	if (is_kernel_in_hyp_mode()) {
+		pr_warn("Protected KVM not available with VHE\n");
+		return false;
+	}
+
+	return true;
+}
+#endif /* CONFIG_KVM */
+
 /* Internal helper functions to match cpu capability type */
 static bool
 cpucap_late_cpu_optional(const struct arm64_cpu_capabilities *cap)
@@ -1794,6 +1810,12 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
 		.field_pos = ID_AA64PFR0_EL1_SHIFT,
 		.min_field_value = ID_AA64PFR0_EL1_32BIT_64BIT,
 	},
+	{
+		.desc = "Protected KVM",
+		.capability = ARM64_KVM_PROTECTED_MODE,
+		.type = ARM64_CPUCAP_SYSTEM_FEATURE,
+		.matches = is_kvm_protected_mode,
+	},
 #endif
 	{
 		.desc = "Kernel page table isolation (KPTI)",

arch/arm64/kvm/arm.c

@@ -1771,7 +1771,9 @@ int kvm_arch_init(void *opaque)
 	if (err)
 		goto out_hyp;
 
-	if (in_hyp_mode)
+	if (is_protected_kvm_enabled())
+		kvm_info("Protected nVHE mode initialized successfully\n");
+	else if (in_hyp_mode)
 		kvm_info("VHE mode initialized successfully\n");
 	else
 		kvm_info("Hyp mode initialized successfully\n");
@@ -1806,6 +1808,11 @@ static int __init early_kvm_mode_cfg(char *arg)
 }
 early_param("kvm-arm.mode", early_kvm_mode_cfg);
 
+enum kvm_mode kvm_get_mode(void)
+{
+	return kvm_mode;
+}
+
 static int arm_init(void)
 {
 	int rc = kvm_init(NULL, sizeof(struct kvm_vcpu), 0, THIS_MODULE);